1. Field of the Invention
This invention relates generally to the art of injection molding and more particularly to an improved injection mold assembly.
2. Prior Art
One common type of injection mold has a central mold member with opposite faces containing open cavities, core plates at opposite sides of the mold member having cores which project into the cavities to form closed mold cavities when the mold is closed, and stripper plates between the mold member and core plates. During a typical molding cycle, the mold is closed and plastic molding medium is forced into the mold cavities under pressure to fill the space between the cores and the cavity walls. After cooling, the mold is opened by moving the core and stripper plates away from the central mold member. The molded articles adhere to the cores and are retracted with the latter from the mold cavities. The final step of the molding cycle involves ejecting or stripping the molded articles from the cores by moving the stripper plates away from the core plates toward the outer ends of the cores.
Initially, the mold opening and core stripping functions were performed without the aid of any means for positively synchronizing the functions. This method of mold actuation has certain disadvantages. A major disadvantage, for example, resides in the fact that the opening movement of the mold plates, i.e., core and stripper plates, does not occur precisely in unison with the result that some of the medium extruded between the contacting mold surfaces. This extrusion damages the mold and often results in improperly formed molded articles and substantial "flash" on the articles which must be removed. In some cases, this problem was aleviated to some degree by utilizing sophisticated hydraulic and electronic mold actuating and timing systems. However these systems substantially increased the cost and complexity of the molds and molding machines. U.S. Pat. No. 3,767,352 discloses a mechanical linkage arrangement for synchronizing the opening and closing movement of the core and stripper plates. This linkage arrangement also has certain disadvantages, however.